1. Field of the Invention
The present invention relates to a fusing device of an image forming apparatus and method thereof. More particularly, the present invention relates to a fusing device of an image forming apparatus and method thereof which locally heats a fusing nip area.
2. Description of the Related Art
In general, a copier, a printer, a facsimile, and a multifunctional device which provides all functions of the copier, the printer, and the facsimile, have a printing function in common. These devices are referred to as an image forming apparatus.
The image forming apparatus includes a fusing device which heats and presses a sheet of paper onto which a toner image is transferred, melts the powdery toner image on the sheet of paper, and fuses the melted toner image on the sheet of paper. The fusing device includes a heating unit which generates heat, and a pressing roller which forms a fusing nip with the heating unit, applies pressure thereto, and helps the toner melt.
The fusing unit melts the toner when the fusing unit is heated to a predetermined temperature, for example, 180° C. Means for heating the fusing unit include a halogen lamp, a resistive coil, or an induction heating coil.
FIGS. 1 and 2 are cross-sectional views illustrating a conventional induction heating-type fusing device according to an embodiment disclosed in U.S. Pat. No. 6,341,211.
Referring to FIGS. 1 and 2, the fusing device includes a conductive member 12 which is a hollow structure fixed in an unrotated state and melts toner 11 on a sheet of paper 10 thermally, a pressing roller 13 which closely presses the sheet of paper 10 having the toner 11 toward the conductive member 12, a traveling belt 20 which is interposed between the fixed conductive member 12 and the pressing roller 13 and transfers the sheet of paper 10, and a coil 14 which inductively heats the conductive member 12. The pressing roller 13 moves in a direction of an arrow B, and the traveling belt 20 is rotated in a direction of an arrow A as the pressing roller 13 moves in the direction of the arrow B.
The conductive member 12 comprises a hollow pipe and comprises one of a carbon steel pipe, a stainless alloy pipe, an aluminum pipe, and iron.
The pressing roller 13 includes an axial core 15 and a silicon rubber layer 16 formed at a circumference of the axial core 15. The pressing roller 13 is pressed in a direction of the conductive member 12 using a spring member (not shown).
A rectangular core 17 forms a closed magnetic circuit, and a part thereof perforates a hollow portion 12a of the conductive member 12. The coil 14 is wound around the core 17. When a current flows through the core 17, magnetic flux by which an inductive current is generated along a circumferential direction of the conductive member 12 is produced. The core 17 is an iron core used in a general transformer. An insulating layer 22 electrically insulates the coil 14 from the core 17.
FIG. 3 shows the structure of a conventional induction heating-type fusing device according to another embodiment disclosed in U.S. Pat. No. 6,341,211. The same reference numerals are used for the same elements as those of the conventional fusing device, and detailed descriptions thereof will be omitted.
The difference between the embodiment of FIGS. 1 and 2 and the embodiment of FIG. 3 is that the core 17 and the conductive member 12 in the embodiment of FIGS. 1 and 2 have a rectangular shape and, in the embodiment of FIG. 3, a conductive member 12′ is a cylindrical roller. Since the other elements are substantially the same, the same reference numerals are used, and detailed descriptions thereof will be omitted.
In the conventional fusing device, since the conductive members 12 and 12′ are uniformly heated by induction, a heating unit is heated to maintain a temperature required for a fusing operation, and the heat loss is significant. In addition, it is difficult to obtain a uniform fusing property due to heat loss at both ends of the conductive members.